Because madmonk28’s description of “America needs to collapse” is an exaggeration of most of their beliefs. They want America to change significantly in a way that neither party is currently willing to do. A third-party win might bring this change but is unlikely to happen. The other option, and the much more likely option, is for one of the two parties to see that they are going to lose over and over unless they change something, and they move their platform. This is what most of the people that didn’t vote for Harris because she wasn’t progressive enough are hoping for.
The question these people have for the Democratic party is simple. How many times does Donald Trump (or someone just as bad) need to elected before you will nominate Bernie Sanders (or someone like him)? It is extremely common for normal Democrats to refer to this as burning everything to the ground, but these voters feel the same way about normal Democrats. By refusing to nominate a more liberal candidate you are burning everything to the ground (because the moderate will lose).
I have a friend that still, to this day, brings up the question, what part about “Bernie of Bust” was confusing? The message was clear. If the Democrats want to win, nominate Bernie. If the Democrats want the Republicans to win, nominate anyone else (this is what “Bust” meant). And yet, she is continually harassed by her party for not voting for Biden or Harris when they could have simply given her what she was demanding. Blue no Matter Who voters will vote for anyone. They may think Bernie is too extreme but will vote for him anyway. Bernie or Bust voters will not vote for anyone but Bernie. If you want all the votes of these two groups of people only Bernie is an acceptable candidate.
As someone that is not a member of either group (and not emotionally invested in the outcome), I can see her point. If I were to step in and try to manipulate all of you into working together, listening to her, rather than moderate Democrats that will vote for anyone that isn’t Trump, makes the most sense. And yet election after election Democrats like her are ignored.
So it goes back to the original question, how many times does Trump, or someone like him, need to win before the Democratic party will finally call on those voters that are just waiting in their back pocket to vote for them but keep getting ignored by selecting the wrong candidates? Republicans were willing to nominate their most extreme candidate 3 times in a row and he won twice. When will the Democrats realize that their more extreme candidates may be more likely to win than their more moderate ones?
That is the message they are sending by staying home or voting third party. It’s up to us whether we want to hear their message and do something about it or continue to pretend that everyone that didn’t vote or voted for anyone but Harris is the most evil, stupid, racist, (insert any other highly inaccurate falsehood based on total ignorance of anyone that doesn’t think just like us) person alive.